|
Using the Data Dictionary |
|
The PxPlus Data Dictionary can be used for designing database applications and is employed in different ways by PxPlus facilities, such as the Views System, the PxPlus SQL ODBC Driver and NOMADS. However, the primary purpose of the data dictionary is to document the contents of a database so that it can be easily viewed, queried and accessed by an application.
The PxPlus syntax below uses the embedded definition to perform these tasks.
When the definition is embedded in the physical data file, the need for an IOLIST statement in your database application is rendered obsolete. An IOList reference is not required for a READ or WRITE statement.
The usual method for reading data from a data file without an embedded definition would appear as follows:
OPEN (1)"SomeFile"
READ (1)name$,address$,company$
OR
READ (1)IOL=MyIOL
PRINT name$
MyIOL: IOLIST name$,address$,company$
If a data dictionary definition is embedded in the physical file, the same routine could be handled as follows:
OPEN (1,iol=*)"SomeFile" ! OPEN using Data Dictionary
READ (1)
PRINT name$
The IOL= option defines a standard IOList to be used while the file is open. PxPlus uses this IOList for all subsequent file READ, WRITE, EXTRACT or FIND statements where you do not explicitly supply variable lists.
You can also use the REC= option to supply a prefix to be added to all the variables in the IOL=:
Open (1,iol=*,rec="a")"SomeFile" ! OPEN using Data Dictionary
Read (1)
Print a.name$
The * asterisk represents an embedded definition. Use a ^ caret to open a file using an alternate IOList.
|
|
Opening a File: |
OPEN (chan,IOL=*)string$ |
|
|
OPEN (chan,IOL=^)string$ | |
|
|
Displaying the IOList: |
PRINT LST (IOL(chan:*)) |
|
|
PRINT LST(IOL (chan:^)) | |
|
|
Displaying an IOList with External Key: |
PRINT LST (IOL(chan:KEY)) |
Example:
The following program illustrates how to open a file and read its contents using an embedded definition. It uses demo files that were installed with PxPlus. You must be in the path /lib/NOMADS/ for this to work.
00020 BEGIN
00030 OPEN (1,IOL=*)"cstfile" ! Open with data dictionary access
00040 PRINT "Load regular IOLIST "
00050 READ (1,END=0080) ! No reference to IOL required
00060 GOSUB PRINT_RECORD
00070 GOTO 0050
00080 CLOSE (1)
00160 END
00170 PRINT_RECORD:
00180 PRINT "_ "+KEC(1)+"_ "
00190 PRINT "Standard iolist"
00200 PRINT "CST_ID$=",CST_ID$
00210 PRINT "CST_NAME$=",CST_NAME$
00220 PRINT "CST_ADDR$=",CST_ADDR$
00230 RETURN